snd_pcm_channel

Signal the driver to ready the specified channel

Synopsis:

#include <sys/asoundlib.h>

int snd_pcm_channel_prepare( snd_pcm_t *handle, 
                             int channel );

Arguments:

handle: The handle for the PCM device, which you must have opened by calling snd_pcm_open_name(), snd_pcm_open(), or snd_pcm_open_preferred().
channel: The channel; SND_PCM_CHANNEL_CAPTURE or SND_PCM_CHANNEL_PLAYBACK.

Library:

libasound.so

Use the -l asound option with qcc to link against this library.

Description:

The snd_pcm_channel_prepare() function prepares hardware to operate in a specified transfer direction by calling snd_pcm_capture_prepare() or snd_pcm_playback_prepare(), depending on the value of channel.

This call is responsible for all parts of the hardware's startup sequence that require additional initialization time, allowing the final “GO” (either from writes into the buffers or snd_pcm_channel_go()) to execute more quickly.

This function may be called in all states except SND_PCM_STATUS_NOTREADY (returns -EBADFD) and SND_PCM_STATUS_RUNNING state (returns -EBUSY). If the operation is successful (zero is returned), the driver state is changed to SND_PCM_STATUS_PREPARED.

Note: If your channel has underrun (during playback) or overrun (during capture), you have to reprepare it before continuing. For an example, see wave.c and waverec.c in the appendix.

Returns:

EOK on success, a negative errno upon failure. The errno values are available in the errno.h file.

Errors:

Additional information for common error values:

-EINVAL: The state of handle is invalid, an invalid channel was provided as input, or an invalid state change occurred. You can call snd_pcm_channel_status() to check if the state change was invalid.
-EBUSY: Channel is running.
-EIO: Channel was not set to SND_PCM_CHANNEL_PLAYBACK or SND_PCM_CHANNEL_CAPTURE.

Classification:

QNX Neutrino

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	Yes
Thread	Read the Caveats

Caveats:

This function is not thread safe if handle (snd_pcm_t) is used across multiple threads.